Method for providing metallic strip of uniform thickness and flatness



N. TRBOVICH 3,397,566

METHOD FOR PROVIDING METALLIC STRIP OF UNIFORM THICKNESS AND FLATNESS Filed Oct. 22, 1965 ROLLING PRESSURE OR FORCE (POUNDS OR TONS) 2 Sheets-Sheet 1 Lynn MILL STRETCH AND STRIP REDUCTION (INCHES OR MILLIMETERS) Te STRIP ENTRY THICKNESS T0 STRIP OUTPUT. THICKNESS To Tee Te N VEN TOR Jfi'cn yfl/ zaw'c fl a/ 7 M, Z; flea ATTORNEYS N. TRBOVICH 3,397,566 METHOD FOR PROVIDING METALLIC STRIP OF UNIFORM Aug. 20, 1968 THICKNESS AND FLATNESS 2 Sheets-Sheet 2 Filed Oct. 22, 1965 6Ez8 96% 4 KM. mum m R |.l|||| ow m 1 3 m 5 I r M4 J I mm 9v W O W MN\ km Z 1 j I l I ll 0 I 2m 1) 6528 mm wmwzxuzi B I wmmzbfiz E Q mm= Swmmoo E308 'llli IIIIEw HEE 1E5 mm 522 359K mfi wzwjom 6528 6528 I 8 Em m m vm All mmwzvaik ATTORNEYS United States Patent METHOD FOR PROVIDING METALLIC STRIP OF UNIFORM THICKNESS AND FLATNESS Nick Trbovich, East Chicago, Ind., assignor to Inland Steel Company, Chicago, 111., a corporation of Delaware Filed Oct. 22, 1965, Ser. No. 502,173 2 Claims. (Cl. 72-365) ABSTRACT OF THE DISCLOSURE A method for rolling metallic strip of uniform flatness and desired thickness at a given roll stand. Correct for deviations from desired thickness solely by varying the conditions which influence the plastic flow line of the strip. Correct for deviations from uniform flatness solely by adjusting the roll stand to that setting which gives uniform flatness at the desired thickness, and maintain the roll stand at that setting for as long as uniform flatness at the desired thickness can be obtained with that setting.

The present invention relates generally to a method of rolling, either hot or cold, metallic strip, either ferrous or non-ferrous. More particularly, the invention relates to a method and apparatus for providing metallic strip of uniform thickness and flatness.

Metallic strip is conventionally provided in coils of relatively long length which have been subjected to a continuous rolling procedure. It is important that the thickness and flatness of the strip be uniform throughout the coil, as well as uniform from coil to coil in situations where two or more coils are offered as the same product.

A conventional rolling mill contains a number of rolling stands spaced apart along the length of the mill. Each rolling stand reduces or works the strip. The final thickness of a strip is determined by the reduction thereof at a final thickness-determining stand, usually the last stand in a rolling mill. In some prior rolling practices, the strip reduction in the last stand has had to be intentionally limited for better control of strip flatness or shape; but this is not a limitation of the present invention.

A rolling stand typically contains a pair of vertically spaced rolls, and the thickness of the strip is generally determined by the gap or distance between the two spaced rolls. This gap is less than the thickness of the strip approaching the rolls so that the strip must undergo a reduction in thickness as it passes between the rolls. The smaller the gap between rolls, the greater the resulting force in the reduction of a given strip of given entry thickness, and vice versa.

In the rolling of thin strip, the rolls may be faced (i.e., actually in contact) or may be set at what is called a negative gap, a situation in which the rolling stand is prestressed to lessen or compensate for mill stretch (e.g., vertical elongation of the rolling mill housing) and for roll flattening and deflection, all of which may normally occur during strip reduction.

In a typical so-called two-high rolling mill stand, the axial end portions of a roll are supported from below and engaged from above by other portions of the rolling mill stand, but the inter-mediate strip-engaging portion of the roll is not.

When a strip undergoes reduction as a result of being passed between a pair of spaced rolls, a tremendous force is exerted against the intermediate strip-engaging portion of the roll, and the intermediate roll portion undergoes a deflection relative to the axial end-supported portions of the roll. The greater the force, the greater the deflection; and this deflection of the roll is reflected in the strip by a deviation from strip flatness.

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A deviation from strip flatness is manifest by a greater thickness at the center of the strip, as measured across the width of the strip, than at the side edges of the strip, or vice versa, such that the strip will not assume a flat position or, in the more extreme cases, waves or buckles are evident in the strip.

In typical so-called three high, four-high or cluster rolling mill stands, additional rolls are provided to reinforce or back-up the intermediate stripengaging portions of the rolls. While such mill stand construction imparts added rigidity to the mill and stripengaging rolls, it is not, of itself, sufiicient to prevent roll deflection and insure strip flatness under all rolling conditions.

One conventional method which attempts to overcome a deviation in strip flatness resulting from roll deflection is to provide the strip-engaging intermediate portion of a rolling mill roll or rolls (either the strip-engaging or back-up rolls or both) with a built-in curvature or contour. However, a drawback to providing a built-in curvature to the roll is that a given curvature will be effective in providing the desired strip flatness at only a relatively narrow range of rolling forces. Moreover, the roll curvature is affected by other factors such as mill and roll temperature changes and roll wear.

Another conventional method which attempts to overcome a deviation in flatness resulting from roll deflection is to provide heating or cooling at selected zones along the length of the roll body, on either or both of the strip-engaging and back-up rolls, to control the relative roll diameters along the length of the roll body. However, drawbacks to this method include its inflexibility due to impossibility or difliculty of precise control and the extremely long thermal time lags involved.

More recent methods for attempting to control flatness involve the so-called method of hydraulic roll bending. In this method, forces, generally produced by hydraulic mechanisms, are applied at the axial end portions of a roll to resist or induce roll deflection. However, this method has the drawbacks of involving additional installation and maintenance costs and of more diflicult integration into the basic control and regulating scheme of the rolling mill control system.

In conventional present-day rolling mills, means are generally provided for continuously measuring the thickness of the strip as it leaves a rolling mill stand, and a measured deviation from the desired strip thickness generally actuates a mechanism for adjusting the gap between the rolling mill rolls to compensate for the deviation in strip output thickness from that desired. This correction may be either an initial or a subsequent correction. However, while such roll gap correction will restore the desired thickness, it also causes a change in rolling force and a corresponding change in roll deflection with its concomitant effect on strip flatness or shape.

Thus, for rolling operations in which it is necessary to periodically adjust the roll gap, so as to compensate for periodic deviations in strip thickness from that desired, the end result may be a strip having the desired uniformity of thickness, but the strip will not have the desired uniformity of flatness or shape.

Inasmuch as commercial tolerances for thickness deviations are more liberal than those for flatness deviations, it is highly important to utilize a system which controls both thickness and flatness, as embodied in the present invention.

The present invention provides a method and apparatus for obtaining the desired strip thickness and the desired strip flatness, both at the same time, and for maintaining the desired thickness and flatness throughout the rolling operation. The resulting product has uniform thick- 3 ness-and flatness along the entire length of the product, with no variation in a coil or from coil to coil.

This is accomplished, in accordance with the present invention, by (l) adjusting the roll gap or setting at the rolling mill stand until the desired strip flatness, suiting the particular strip product and the particular mill and roll. characteristics, is obtained and (2) adjusting, in conjunction with adjustment of the roll setting, at least one rolling condition selected from the group consisting essentially of strip speed, strip tension, strip coefiicient of rolling friction ,(generally by control of strip or rolling lubricant) and the thickness of the strip entering the stand. One or more of this group of conditions is adjusted until not only the desired strip flatness but also the desired strip thickness is initially obtained. Then the roll setting at which the desired thickness and flatness are obtained is noted, and this setting is maintained throughout the rest of the operation, as long as flatness continues to be satisfactory.

The initial adjustment of the rolling conditions to the initial desired values are easily within the skill of experienced rolling mill operators.

As the rolling operation proceeds, any change in output thickness, for a given roll setting, is accompanied by a change in rolling force. Therefore, either or both rolling force or strip output thickness can be measured continuously to indicate any deviation from desired strip thickness, and any deviation in these measurements from predetermined desired values can be used, either individually or in combination, to actuate means for automatically restoring the desired thickness.

However, in compensating for the change in thickness, the roll setting is not changed as long as flatness is satisfactory. Instead, a change is made in at least one of the above-noted group of strip rolling conditions until the thickness or rolling force measurement has returned to the desired value, indicating the return of the desired thickness. When this has occurred, the above-noted group of rolling conditions is maintained at the changed values, as long as there are no additional deviations in the abovenoted thickness-indicating measurements.

Because adjustments made to return to desired strip thickness do not include a change in the initial roll setting or gap, there is no change caused in the rolling force, no change in roll deflection and no problem in maintaining flatness.

The methods and apparatus embodied in the present invention for the control of both thickness and flatness differ from the socalled gagemeter or load cell type of control which corrects only thickness deviations. In the gagemeter method, load cells on the rolling stand are used to measure rolling force at that stand, and any deviation in output thickness from the stand is indicated by a change in the measured force. (For example, an increase in thickness, for a given roll setting, is indicated by an increase in measured rolling force.) When a deviation in thickness is noted, the roll setting atthe stand is changed to restore the desired thickness, resulting in a further change in rolling force. Essentially, the gagemeter method' operates to maintain constant the sum of the mill stretch and the unloadedroll setting. The changes in roll setting, required by the gagemeter method, result in-a variation in rolling force and consequent undesirable variations in roll deflection and strip flatness.

The methods and apparatus of the present invention differ from conventional automatic gauge control systems using thickness-measuring devices as the primary sensing and controlling element. One major difference is that conventional gauge control systems are designed and operated with little or no consideration of strip flatness, nor is consideration given to the simultaneous and coordinated control of both'thickness and flatness, as is the case in the present invention. Instead, conventional prior gauge control systems correct for thickness deviations by changing, either initially or subsequently, the roll setting or gap;

and such a change results in an undesirable change of rolling force, of roll deflection and of strip flatness.

Other features and advantages are inherent in the method and apparatus claimed and disclosed or will become apparent to those skilled in the art from the following description in conjunction with the accompanying drawings wherein:

FIGURE 1 is a graph plotting rolling pressure or force against mill stretch and strip reduction; and

FIGURE 2 is a schematic illustration of an embodiment of apparatus in accordance with the present invention.

Referring initially to FIGURE 1, the line D intersecting the abscissa at T corresponds to the desired output thickness of the metallic strip. The point T on the abscissa is the thickness of the strip as it enters the rolling mill stand. The point I on the abscissa corresponds to the initial or unloaded setting of the rolls, or the gap between the rolls of the rolling mill stand.

It should be noted that as a strip undergoes reduction between a pair of rolling mill rolls, the rolling mill stand undergoes a stretch so that the gap between the rolls increases during the reduction of the strip. (Stretch comprises an actual increase in the length of the mill housing and/ or roll flattening and/ or deflection and other dimensional changes within the mill due to the applied rolling force.) Other considerations aside from stretch are also involved in determining the gap between rolls. These include the change in roll bearing lubricating oil film thickness with a change in speed, which, for a given roll setting, changes the roll gap and therefore effects strip reduction and consequently the rolling force and mill stretch.

Accordingly, the gap between the rolls is not set at a distance corresponding to T but is set at a distance less than T 0 to compensate for the stretch, etc., in the mill during reduction of the strip. In fact, as noted previously, in the rolling of thin strip, the initial gap may be zero or even negative (a situation in which the mill stand is in a prestressed condition).

The line B, intersecting both T and strip output thickness line D, is the plastic flow line for the strip. Line A, between a point, such as J, corresponding to the initial setting of the rolling mill rolls and a point, such as C, on the strip output thickness line D, corresponds to the mill modulus of elasticity or stretch. For a given mill stand and roll combination, this mill modulus or stretch line maintains essentially the same slope.

The rolling mill modulus line A and the strip plastic flow line B intersect at a point C, and this point is indicative of both the strip output thickness (line D) and the rolling force (line E). This point of intersection can be varied by varying the initial roll setting or by varying the strip entry thickness or by varying one or more of the rolling conditions which influence the slope of the plastic flow line of the strip. These last described conditions include strip speed, strip tension and strip coefficient of rolling friction. The friction coefi'icient is generally manipulated by controlling the amount, type, temperature and application pattern of the strip coolant or lubricant, though strip speed is also a factor in rolling friction. Strip chemistry, metallurgy, dimension, temperature and strip hardness (which may depend upon prior working, reduction or heat-treating) also influence the slope of the plastic flow line.

Other factors alfecting rolling force, such as roll diameter and hardness and strip and roll surface condition, need not be considered for purposes of this discussion.

At some point along the desired output thickness line D, there is a rolling pressure or force, suitable to the particular strip, mill and roll characteristics, which will provide not only the desired strip final thickness but will also provide the desired strip flatness. In accordance with the method of the present invention, the rolling mill operator initially adjusts the roll setting or gap, and

the group of conditions which influence the strip plastic flow line, including strip entry thickness, until he obtains a strip having both the desired thickness and the desired flatness. For purposes of illustration, this is point C on line D; and line E represents the rolling force which will provide the desired strip flatness. In this ideal situation, the mill stand modulus or stretch line is represented by line A, and the plastic flow line of the strip is represented by line B.

Assuming a rolling mill operation in which the conditions described in the previous paragraph are in effect, if the strip :being rolled then undergoes a change, or non-uniformity, of chemistry or a change in hardness, or if there is a change in certain other factors affecting strip thickness or flatness, the plastic flow line of the strip will change, e.g., from line B to dotted line F. Under these conditions, with a constant roll setting I and a corresponding mill modulus or stretch line A, line A intersects line F at point K, and the output thickness of the strip changes from line D to dotted line G, a deviation from the desired strip thickness.

The conventional method of compensating for this change in strip thickness is to change or decrease the roll setting or gap, e.g., from J to M, so as to return the strip thickness to the desired value. This would change the mill modulus or stretch line from A to dotted line I, a line which intersects the plastic flow line F at line D; and the point where line I intersects plastic flow line F in line D is at L, which has a corresponding rolling pressure or force defined by dotted line P. Because of the change in roll setting from I to M, and the corresponding change in rolling force from line B to line P, there will be a change in roll deflection and the strip which was in the desired condition of flatness at rolling force E is no longer in the desired condition of flatness.

In accordance with the present invention, the roll setting is not changed from J to M, but is maintained constant at that setting (1 providing the desired flatness. Accordingly, no change in rolling force occurs. The only change that is made is to change those rolling conditions which influence the strip plastic flow line. These include, as discussed previously, strip tension, strip speed and strip coeflicient of rolling friction; and all of these conditions influence the slope of the strip plastic flow line. One or more of these conditions is changed to return the plastic flow line from slope F to slope B. A return to line B is indicated by a return of the rolling force measurement to line E and/ or a return of the thickness measurement to line D'.

Another way of assuring that the strip plastic flow line will intersect the mill modulus line A at point C on line D, is to change the strip entry thickness from T to a different value, e.g., T Changing the strip entry thickness, either alone or in conjunction with a change of the conditions which influence the slope of the strip plastic flow line, will provide a new plastic flow line, represented by the dash-dot line N. The strip entry thickness can be adjusted by, among other things, varying the conditions of reduction prior to the rolling mill stand into which a strip of changed thickness is desired to be introduced.

The possibility of changing the strip entry thickness for the control of both thickness and flatness, as embodied in the present invention, is another contrast to some prior methods of conventional automatic gauge control systems which, to facilitate control of final or output thickness, strived, by some prior or supplemental regulating scheme, to hold entry thickness constant.

The foregoing description considered the eflect of, and corrective measures for, a change in slope of the strip plastic flow line which tended to increase the output thickness and the rolling force. For a change in slope of the strip plastic flow line which tends to decrease the output thickness and the rolling force, a similar eflect is noted and similar corrective measures (adjust slope of strip plastic tlow line or strip entry thickness) are taken.

If there is a change, either an increase or a decrease, in strip entry thickness, the eifect is the same as a change in the slope of the strip plastic flow line. Corrective measures to provide the desired thickness and flatness, in accordance with the present invention, include adjusting the slope of the strip plastic flow line so that it intersects line A at C, or taking such steps upstream of the final rolling stand as will return the strip entry thickness to what it was previously.

In connection with FIGURE 1, it might be noted that the mill modulus line and the strip plastic flow line are idealized; and, in actual practice, these lines may not be straight lines but may be curved lines.

The changes necessary to return the plastic flow line to an intersection with the mill modulus line at point C, or the changes necessary to make an equivalent correction in strip entry thickness, can be accomplished automatically utilizing apparatus illustrated in FIGURE 2, which shows, in simplified and diagrammatic form, an embodiment of this invention.

In FIGURE 2, for purposes of illustration, two rolling mill stands 9, 10 are shown. In this illustration, the second stand 10 is used for controlling output thickness and flatness.

The first stand 9 has a pair of work rolls 11, 12 driven by a roll drive 13 controlled from 14; and the gap between rolls 11 and 12 is determined by the setting of a screw or hydraulic mechanism 15 driven by 16 and controlled from 50.

The second stand 10' has a pair of work rolls 17, 18 driven by a roll drive 19 controlled from 20; and the gap between rolls 17 and 18 is determined by the setting of a screw or hydraulic mechanism 21 driven by 22 and controlled from 51 which, in turn, is manually operated to provide the initial desired flatness in the strip.

Rolls 11, 12 of first stand 9 and rolls 17, 18 of second stand 10 reduce a metallic strip 23 unwound from a coil 24 mounted on a reel 25 driven by a reel drive 26 controlled :from 27. As noted previously, in prior art methods the reduction in the final or controlling stand has oftentimes been limited so as to minimize force variations which have a deleterious effect on strip shape and flatness, but such limitation or restriction is not a necessary condition of the present invention.

Strip 23 is rewo-und, after reduction, in a coil 28 mounted on a reel 29 driven by a reel drive 30 controlled from 31.

The output thickness of strip 23 as it leaves stand 10 is measured by conventional means, such as X-ray device 3 2.

The rolling force or pressure at stand 10 is measured by conventional means 33 which may be a load cell device or a hydraulic pressure measuring and controlling device. 1

FIGURE 2 shows only one thickness-measuring device 32, and only one force-measuring device 33. However, two or more thickness-measuring devices can be used, e.g., by installing other thickness-measuring devices upstream of roll stand 10'; and two or more force-measuring devices can be used by installing a force-measuring device at each stand of the rolling mill. Such additional devices can, in various methods, be used as refinements of the control proposed in the present invention, and/ or they can be used for other purposes.

As will be evident from a study of FIGURE 1, any deviation from the point C (the ideal control point for both thickness and flatness) will be reflected by a change in both output thickness and rolling force. Thus, either thickness-measuring device 32 or rolling force rneasuring device 33 can be used alone as the primary sensing device to recognize a deviation from the ideal control point, or the two can be used together.

The signal from thickness-measuring device 32 and/or the signal from force-measuring device 33 are transmitted to a conventional signal selector and comparator device 34, where these signals are compared with the predetermined ideal or set points. If there is a deviation between the measured value and the set value, the deviation is manifest as a signal which is transmitted to a conventional control programmer 35. The set point for desired output thickness is immediately available from the thickness ordered by the customer, and this is initially set into comparator device 34, e.g., manually. The set point :for the rolling force required to give the desired flatness is determined at an early stage by the rolling mill operator and is then introduced into comparator device 34, e.g., manually.

The control programmer 35 can be set, wired or programmed to make individual corrections, described below, in any desired number or steps, of any desired magnitude and in any desired sequence, or to make multiple corrections in any desired combination, whichever will best fit the particular mill or the preferred rolling practice.

For example, the control can be utilized to transmit the proper signals to a strip lubricant control device 36, to change the type, amount, temperature or application pattern of the strip coolant or lubricant which flows from a supply reservoir (not shown) through control device 36 to spray nozzles 37 for distribution on strip 23. This in turn will influence the coefficient of rolling friction for the strip. While only one set of spray nozzles 37 are shown, it is understood that two or more sets can be used and at various other locations.

The control can also be utilized to change the striprolling speed by transmitting the proper signals to a conventional master speed reference and control device 38 which in turn is connected to and operates individual drive controls 31, 20, 14, 27. These in turn influence the speed of strip 23.

The control can also be utilized to change the strip tension by transmitting the proper signals to a conventional tension reference and control device 39. Device 39 in turn is connected to and influences the operation of drive control 14 for mill stand 9 so as to change the tension of the strip portion between mill stands 9' and 10, in a conventional manner. A conventional strip tension-measuring device 40 can be incorporated in the tension control arrangement to monitor tensions and send a signal, corresponding to tension, to control device 39 for the purpose of maintaining tension limits. While FIGURE 2 shows direct tension control on one strip portion only, between stands 9 and 10, tension can also be directly controlled on two or more strip portions.

The control can further be utilized to change the strip entry thickness into stand by transmitting the proper signals to the roll setting control device 50 for stand 9 so as to change the output thickness from stand 9. While FIGURE 2 shows a roll setting control for only one stand prior to final stand 10, it is understood that roll setting changes can be made on any or all stands prior to the final or controlling stand.

The above-described changes in rolling conditions can be made in any desired number or sequence or in any desired combination. Combinations of changes can be sequenced on the basis of the guides, restraints or limits for the lead-ofl change of a combination of changes. For example, if an initial change 'were made in strip tension, and then a maximum or minimum tension limit is reached, the control (device 35) can be prearranged to initiate a change in some other condition, e.g., a roll setting change on a stand, such as 9, preceding the final or control stand 10.

Such corrections or changes, in the desired sequence or combination, are made until the signal from thickness measuring device 32 and/or the signal from force-measuring device 33 are restored to their predetermined desired values, as determined by comparator 34.

The method and apparatus of the present invention may be utilized in a fully automated system, wherein the measuring devices and the strip rolling condition controls would be associated with a computer which is set, wired and programmed to obtain and maintain correct strip thickness and flatness. A fiurther refinement would have the computer calculate and predetermine set and reference values, to minimize or eliminate the trial and error method required of operators to establish the initial conditions providing desired thickness and flatness.

In another embodiment of the method and apparatus of the present invention, if the correct output thickness (e.g., line D) is being obtained, but shape or flatness is incorrect, the roll setting or gap can be changed to obtain correct flatness. This can be done by manually operating control 51 for the screw drive 22 until desired flatness is observed. Compensating changes will then be automatically made to the previously noted rolling conditions (strip speed, tension, friction coeflicient or entry thickness) sep arately or in combination, until both the desired flatness and thickness are obtained. This will result in the same output thickness, but at a different rolling force.

More specific-ally, assume that more roll deflection is required to give the required strip flatness (that is, produce less strip center reduction or more strip edge reduction); and that the desired flatness can be obtained at a rolling force corresponding to line P. In such a case, the roll gap is reduced from point I to point M, and this produces a corresponding mill modulus or stretch line I. However, the original plastic flow line B intersects line I at point R, resulting in both incorrect thicknes and flatness. Therefore, changes are made to the previously noted rolling conditions (strip speed, tension and friction coeflicient) so as to change the slope of the plastic flow line from B to F. Because plastic flow line F and mill modulus line I intersect at line D, the same strip output thickness as was previously obtained is still obtained, and the desired flatness is also obtained.

Or, instead of changing the slope of the plastic flow line from B to F, the strip entry thickness can be increased to provide a new plastic flow line (parallel to line B) intersecting line I at point L (on line D), so as to restore the desired output thickness for the new condition producing the required flatness. Thereafter, utilizing the control described in conjunction with FIGURE 2, the conditions will be maintained to provide uniform thickness and flatness, as previously described.

If changes in the rolling conditions and/or strip entry thickness are actuated in response to a deviation between measured strip thickness and the control strip thickness set into comparator 34, the changes will take place automatically.

If the changes are actuated only in response to a deviation between measured rolling force and the control rolling force set into comparator 34, a new control rolling force (corresponding to the new roll gap setting) will have to be set into comparator 34 before the changes in rolling conditions and/or strip entry thickness will take place automatically. This can be done, for example, by the operator, as previously explained in connection with the original roll force setting on comparator 34. Until a new control rolling force is set in comparator 34, the changes would be manually made.

The immediately preceding example considered the case where more roll deflection was required to give the desired flatness. Where less roll deflection is required to give desired flatness, the same rolling conditions are changed as were changed in the preceding example to give desired thickness, except that the changes are made to produce the opposite effect on thickness.

In the previously described embodiments, the initial desired flatness or the subsequent flatness correction (in a situation where correct thickness is being obtained but correct flatness is not) are effected by manual operation of control 51 for screw 21 on stand 10, and flatness is determined by the visual observation of an operator.

In those cases where control 51 is manually operated, it may also be automatically operated by a strip flatness or shape detector (shown in dash-dot lines at 41), when this type of device becomes commercially available. Detector 41, located downstream of stand 10, detects deviations from desired flatness in strip 23 and signals control 51 to either increase or decrease, as the case may be, the setting or gap between rolls 17, 18. This changes the rolling force and roll deflection to provide the desired flatness. Detector 41 eliminates both manual setting of control 51 and visual observation of strip flatness.

When thickness is to be regulated in response to a rolling force measurement, a signal from detector 41, proportional to the roll gap change, may also be sent to comparator 34, as a new reference for the signal from load or rolling force measuring device 33; and the new force reference from detector 41 is compared with the rolling force measurement from 33 for purposes of actuating such changes in the rolling conditions as are necessary to correct for deviations in strip thickness, as previously explained. Flatness detector 41 does not signal control 51 to change the roll gap, which is maintained constant, when corrections must be made for deviations in strip thickness.

Although only one flatness detector is shown in FIG- URE 2, other flatness detectors may be used at other locations upstream of stand 10.

In summary, the roll gap or setting of the final or controlling stand is changed only when it is necessary to make this change to achieve proper shape or flatness, and not to compensate for changes in output thickness. Changes in thickness are compensated by changing only the other rolling conditions, as previously described.

Aside from flatness detector 41, all of the apparatus components illustrated diagrammatically in FIGURE 2 are conventional and are available commercially. Control programmer 35 may be provided with such conventional system sets, limits, references, feedbacks, etc., as may be necessary to optimize automatic control of the system, such provisions being within the skill of the art.

Thus, the present invention may be used to compensate automatically for variations in both output thickness and flatness, to produce the desired strip characteristics. To amplify, this invention provides for control of both the rolling force (and consequently the roll deflection) and the strip thickness, once satisfactory initial output thickness and flatness are obtained, and this represents point control (point C of FIGURE 1); whereas, conventional gauge control methods merely accept any rolling conditions which provide the desired output thickness, irrespective of flatness, and this represents merely line control (any point on line D of FIGURE 1). By way of further amplification, conventional automatic gauge control may be considered as longitudinal thickness control (or control of thickness along the length of the strip); whereas, this invention combines longitudinal thickness control with transverse thickness control (or control of thickness across the width of the strip).

While, for purpose of simplification, this discussion covered only strip rolling, it is understood that the method and apparatus embodied in the present invention are equally applicable to any rolling process benefiting from both longitudinal and transverse control of thickness.

The above-described method and apparatus are intended for use in either hot rolling or cold rolling operations and on either ferrous or non-ferrous metals. This invention may be used on either single-stand mills (which would preclude changes in strip entry thickness), reversing or non-reversing, or on multiple-stand mills. On multiple-stand mills, the invention may be used on any one or more of the rolling stands involved, but the invention is most particularly useful on the last stand of a multiple-stand mill, which stand is the predominant one from the standpoint of regulating and controlling output thickness and flatness or shape.

The foregoing detailed description has been given for simplicity and clea-rness of understanding only, and no unnecessary limitations should be understood therefrom, as modifications will be obvious to those skilled in the art.

What is claimed is: 1. In a method for rolling metallic strip of desired thickness and uniform flatness at a given roll stand, the steps comprising:

correcting for deviations from said desired thickness solely by varying at least one of the conditions which influence the plastic flow line of said strip;

correcting for deviations from uniform flatness solely by adjusting said roll stand to that setting which gives uniform flatness at said desired thickness;

and maintaining said roll stand at said setting for as long as uniform flatness at said desired thickness can be obtained with said setting;

said flatness correcting step being performed only when uniform flatness cannot be obtained at said desired thickness with a setting then being used.

2. A method as recited in claim 1 wherein:

said conditions which influence the plastic flow line of said strip include the strip speed, the strip coeflicient of rolling friction, the thickness of the strip entering said roll stand, and the strip tension;

said thickness correcting step comprising varying a combination of said conditions.

References Cited UNITED STATES PATENTS 2,903,926 9/ 1959 Reichl 728 2,949,799 8/ 1960 Walker 72234 2,972,268 2/ 1961 Wallace 728 2,972,269 2/ 1961 Wallace 72205 3,006,225 10/1961 Mamas.

3,030,836 4/ 1962 Gochenour 72--234 3,081,651 3/ 1963 Roberts 729 3,150,548 9/ 1964 Roberts 7216 3,169,420 2/1965 Stone et al. 729205 3,213,655 10/1965 Reid 7211 3,290,912 12/1966 Reid 72-9 CHARLES W. LANHAM, Primary Examiner.

A. RUDERMAN, Assistant Examiner. 

